Melatonin Production Accompanies Arousal from Daily Torpor in Siberian Hamsters

2003 ◽  
Vol 76 (4) ◽  
pp. 577-585 ◽  
Author(s):  
Jennie E. Larkin ◽  
Steven M. Yellon ◽  
Irving Zucker
Keyword(s):  
Daily Torpor ◽  
Siberian Hamsters ◽  
Melatonin Production

Control of torpor and body weight patterns by a seasonal timer in Siberian hamsters

1989 ◽  
Vol 257 (1) ◽  
pp. R142-R149 ◽  
Author(s):  
T. J. Bartness ◽  
J. A. Elliott ◽  
B. D. Goldman
Keyword(s):  
Body Weight ◽  
Food Intake ◽  
Implant Removal ◽  
Daily Torpor ◽  
Short Day ◽  
Siberian Hamsters ◽  
Long Day ◽  
Preparatory Phase ◽  
Pelage Color ◽  
Seasonal Responses

Two experiments were designed to assess whether the short-day-induced patterns of shallow daily torpor, body weight, and other seasonal responses (food intake and pelage pigmentation) exhibited by Siberian hamsters (Phodopus sungorus sungorus) are under the control of a "seasonal timekeeping mechanism" that is independent of reproductive status [testosterone, (T)]. We examined whether the patterning and expression of these seasonal responses were altered by decreases in serum T that accompany gonadal regression during the first 8 wk of short-day exposure (i.e., the "preparatory phase" of the torpor season) or by experimental increases in serum T after this phase. Short-day-housed, castrated hamsters bearing T implants had long-day levels of the hormone and did not exhibit torpor. Appropriate seasonal patterns and levels of torpor, body weight, pelage color stage, and food intake were exhibited after T implant removal although serum T was clamped to long-day levels during the preparatory phase. In animals that were gonad intact during the preparatory phase and were subsequently castrated and given T implants, torpor did not occur as long as the implants were in place. However, the patterns and levels of daily torpor, food intake, and body weight rapidly returned to appropriate seasonal values compared with the castrated, blank-implanted controls on T implant removal; these effects occurred whether the T implants were removed when torpor frequency was increasing, at its peak, or decreasing across the torpor season. T did not affect pelage color stage under any condition.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals The Chemistry of Cold: Mechanisms of Torpor Regulation in the Siberian Hamster

Physiology ◽  
2016 ◽  
Vol 31 (1) ◽  
pp. 51-59 ◽  
Author(s):  
Ceyda Cubuk ◽  
Jonathan H. H. Bank ◽  
Annika Herwig
Keyword(s):  
Physiological State ◽  
Daily Torpor ◽  
Brain Areas ◽  
Siberian Hamster ◽  
Siberian Hamsters ◽  
Save Energy

Siberian hamsters use spontaneous daily torpor, a state of hypometabolism and hypothermia, to save energy during winter. Multiple neuroendocrine signals set the scene for spontaneous torpor to occur, and several brain areas have been identified as potential sites for torpor regulation. Here, we summarize the known mechanisms of a fascinating physiological state in the Siberian hamster.

Cardiac dynamics during daily torpor in the Djungarian hamster (Phodopus sungorus)

2008 ◽  
Vol 294 (2) ◽  
pp. R639-R650 ◽  
Author(s):  
Alexander Mertens ◽  
Oliver Stiedl ◽  
Stephan Steinlechner ◽  
Michael Meyer
Keyword(s):  
Conduction Block ◽  
Phodopus Sungorus ◽  
Control Mechanisms ◽  
Daily Torpor ◽  
Qrs Complex ◽  
Siberian Hamsters ◽  
Cardiac Dynamics ◽  
St Segment ◽  
Electrocardiogram Ecg ◽  
Ventricular Conduction

Djungarian or Siberian hamsters ( Phodopus sungorus) acclimated to short photoperiod display episodes of spontaneous daily torpor with metabolic rate depressed by ∼70% and body temperature (Tb) reduced by ∼20°C. To study the cardiovascular adjustment to daily torpor in Phodopus, electrocardiogram (ECG) and Tb were continuously recorded by telemetry during entrance into torpor, in deep torpor, and during arousal from torpor. Minimum Tb during torpor bouts was ∼21°C, and heart rate, ∼349 beats/min at euthermy, displayed marked sinus bradyarrhythmia at ∼70 beats/min. Arousal was typically completed within ∼40 min, followed by a sustained posttorpor inactivity tachycardia (∼540 beats/min). The absence of episodes of conduction block, tachyarrhythmia, or other forms of ectopy throughout the torpor cycle demonstrates a remarkable resistance to arrhythmogenesis. The ECG morphology lacks a distinct isoelectric interval following the QRS complex, and the ST segment resembles the ECG pattern in mice, with a prominent fast transient outward K+ current ( Ito,f) determining the early phase of ventricular repolarization. During low-temperature torpor, the amplitudes of the QRS complex substantially increased, suggesting that in the euthermic state the terminal portion of ventricular depolarization is fused with the beginning of repolarization, low Tb acting to decorrelate the superposition between depolarization and repolarization by delaying the repolarization onset. Atrioventricular and ventricular conduction times were prolonged as function of Tb. In contrast, the QT vs. Tb relationship showed marked hysteresis indicating the operation of nonlinear control mechanisms whereby the rapid QT shortening during arousal results from additional mechanisms (probably sympathetic stimulation) other than temperature alone.

Daily torpor in the absence of the suprachiasmatic nucleus in Siberian hamsters

1992 ◽  
Vol 263 (2) ◽  
pp. R353-R362 ◽  
Author(s):  
N. F. Ruby ◽  
I. Zucker
Keyword(s):  
Suprachiasmatic Nucleus ◽  
Food Restriction ◽  
Temporal Organization ◽  
Daily Torpor ◽  
Short Day ◽  
Siberian Hamsters ◽  
Random Fashion ◽  
Before And After ◽  
Ad Libitum ◽  
Short Days

Siberian hamsters express torpor spontaneously after several weeks of exposure to short days. In long days, torpor is expressed only when food intake is restricted. Hamsters maintained in a long photoperiod (16 h light/day) at 15 degrees C expressed daily torpor during food restriction both before and after bilateral ablation of the suprachiasmatic nucleus (SCN). Hamsters housed in short days (8 h light/day, ambient temperature 15 degrees C) and fed ad libitum displayed torpor before, but not after, ablation of the SCN (SCNX). Torpor was reinstated in all short-day SCNX hamsters during postoperative food restriction and persisted in several animals even after ad libitum feeding was reinstated. Torpor was entrained to the light-dark cycle in both long- and short-day hamsters preoperatively but appeared to occur in a temporally random fashion in SCNX animals. SCNX hamsters, unlike control animals, displayed multiple torpor bouts per 24 h. The SCN is not essential for the expression of torpor but plays a crucial role in its temporal organization.

The Effects of Dietary Cholesterol on Metabolism and Daily Torpor Patterns in Siberian Hamsters

2014 ◽  
Vol 87 (4) ◽  
pp. 527-538 ◽  
Author(s):  
Małgorzata Jefimow ◽  
Maciej Ostrowski ◽  
Anna Jakubowska ◽  
Michał S. Wojciechowski
Keyword(s):  
Dietary Cholesterol ◽  
Daily Torpor ◽  
Siberian Hamsters

Monosodium glutamate-induced arcuate nucleus damage affects both natural torpor and 2DG-induced torpor-like hypothermia in Siberian hamsters

2008 ◽  
Vol 294 (1) ◽  
pp. R255-R265 ◽  
Author(s):  
Kimberly M. Pelz ◽  
David Routman ◽  
Joseph R. Driscoll ◽  
Lance J. Kriegsfeld ◽  
John Dark
Keyword(s):  
Body Temperature ◽  
Body Fat ◽  
Food Restriction ◽  
Arcuate Nucleus ◽  
Monosodium Glutamate ◽  
Daily Torpor ◽  
Dark Cycle ◽  
Leptin Receptors ◽  
Fat Reserves ◽  
Siberian Hamsters

Siberian hamsters ( Phodopus sungorus) have the ability to express daily torpor and decrease their body temperature to ∼15°C, providing a significant savings in energy expenditure. Daily torpor in hamsters is cued by winterlike photoperiods and occurs coincident with the annual nadirs in body fat reserves and chronic leptin concentrations. To better understand the neural mechanisms underlying torpor, Siberian hamster pups were postnatally treated with saline or MSG to ablate arcuate nucleus neurons that likely possess leptin receptors. Body temperature was studied telemetrically in cold-acclimated (10°C) male and female hamsters moved to a winterlike photoperiod (10:14-h light-dark cycle) ( experiments 1 and 2) or that remained in a summerlike photoperiod (14:10-h light-dark cycle) ( experiment 3). In experiment 1, even though other photoperiodic responses persisted, MSG-induced arcuate nucleus ablations prevented the photoperiod-dependent torpor observed in saline-treated Siberian hamsters. MSG-treated hamsters tended to possess greater fat reserves. To determine whether reductions in body fat would increase frequency of photoperiod-induced torpor after MSG treatment, hamsters underwent 2 wk of food restriction (70% of ad libitum) in experiment 2. Although food restriction did increase the frequency of torpor in both MSG- and saline-treated hamsters, it failed to normalize the proportion of MSG-treated hamsters undergoing photoperiod-dependent torpor. In experiment 3, postnatal MSG treatments reduced the proportion of hamsters entering 2DG-induced torpor-like hypothermia by ∼50% compared with saline-treated hamsters (38 vs. 72%). In those MSG-treated hamsters that did become hypothermic, their minimum temperature during hypothermia was significantly greater than comparable saline-treated hamsters. We conclude that 1) arcuate nucleus mechanisms mediate photoperiod-induced torpor, 2) food-restriction-induced torpor may also be reduced by MSG treatments, and 3) arcuate nucleus neurons make an important, albeit partial, contribution to 2DG-induced torpor-like hypothermia.

Prolactin and testosterone inhibit torpor in Siberian hamsters

1993 ◽  
Vol 264 (1) ◽  
pp. R123-R128 ◽  
Author(s):  
N. F. Ruby ◽  
R. J. Nelson ◽  
P. Licht ◽  
I. Zucker
Keyword(s):  
Food Intake ◽  
Suprachiasmatic Nucleus ◽  
Daily Torpor ◽  
Osmotic Minipumps ◽  
Siberian Hamsters ◽  
Long Day ◽  
Discontinuation Of Treatment ◽  
Plasma Prl

Female Siberian hamsters maintained in a winter photoperiod (8 h light/day) ceased to undergo daily torpor during infusion of prolactin (PRL) from osmotic minipumps; winter torpor was reinstated within 3 days of discontinuation of treatment. By contrast, PRL infusion was ineffective in suppressing daily torpor elicited by restricting food intake in female hamsters housed in a summer photoperiod (16 h light/day). Summer daily torpor was, however, completely inhibited in long-day gonadectomized male hamsters treated with testosterone (T). We suggest that the hyperprolactinemia, which in previous studies is characteristic of hamsters that sustain ablation of the suprachiasmatic nucleus, is incompatible with winter torpor. Summer torpor may be controlled by a mechanism less responsive to variations in plasma PRL concentration. Both winter and summer torpor are inhibited by exogenous T; it remains uncertain, however, whether sustained decreases in endogenous T secretion are as essential for the expression of summer as they are for winter torpor.

Glucoprivation counteracts effects of testosterone on daily torpor in Siberian hamsters

1996 ◽  
Vol 270 (2) ◽  
pp. R398-R403 ◽  
Author(s):  
J. Dark ◽  
D. R. Miller ◽  
P. Licht ◽  
I. Zucker
Keyword(s):  
Energy Savings ◽  
Inhibitory Effect ◽  
Daily Torpor ◽  
Adult Males ◽  
Inhibitory Effects ◽  
Ambient Temperatures ◽  
Siberian Hamsters ◽  
Potent Inhibitory Effect ◽  
Hypometabolic State ◽  
Glucose Analogue

We tested whether 1) glucose availability is a signal for initiation of torpor in male hamsters and 2) glucoprivation can override the inhibitory effects of androgens on daily torpor. Male hamsters maintained at ambient temperatures of 8-16 degrees C were injected with 2-deoxy-D-glucose (2DG), a glucose analogue that interferes with cellular glucose oxidation. 2DG (2,000-2,500 mg/kg body mass) induced torpor within 1 h of treatment in normal adult males in reproductive condition and in those bearing testosterone (T)-filled capsules that produced supraphysiological blood T concentrations; body temperatures were reduced from 37 to 25 degrees C for several hours. Latency to torpor was increased and duration of torpor was decreased in the T-treated hamsters. Food intake decreased substantially both on the day of torpor and on the succeeding day. Glucoprivation appears to counteract the potent inhibitory effect of androgens on torpor and induces a hypometabolic state that results in overall energy savings.

scholarly journals Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal

2015 ◽  
Vol 309 (6) ◽  
pp. R668-R674 ◽  
Author(s):  
Frank Scherbarth ◽  
Victoria Diedrich ◽  
Rebecca A. Dumbell ◽  
Herbert A. Schmid ◽  
Stephan Steinlechner ◽  
...  
Keyword(s):  
Somatostatin Receptor ◽  
Somatostatin Receptors ◽  
Receptor Activation ◽  
The Body ◽  
Receptor Subtypes ◽  
Marginal Effect ◽  
Hormonal Changes ◽  
Daily Torpor ◽  
Siberian Hamsters ◽  
Somatostatin Receptor Subtypes

Siberian hamsters ( Phodopus sungorus) show spontaneous daily torpor only after ∼2 mo in winter-like short photoperiods (SP). Although some SP-induced hormonal changes have been demonstrated to be necessary for the occurrence of seasonal torpor, the whole set of preconditions is still unknown. Recent findings provide evidence that the hypothalamic pituitary growth axis is involved in endocrine responses to SP exposure in the photoperiodic hamsters. To examine whether suppression of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) secretion affects the incidence of daily torpor, we used two somatostatin receptor agonists, pasireotide (SOM230) and octreotide, with different affinity profiles for receptor subtypes. Pasireotide strikingly increased the torpor frequency in male hamsters compared with sham-treated controls, and torpor duration was often increased, which in some cases exceeded 12 h. In contrast, administration of octreotide reduced the body weight of SP hamsters but had only a marginal effect on torpor frequency in males and no effect in females. Together with measured concentrations of circulating IGF-1, the present results strongly suggest that reduced activity of the GH/IGF-1 axis is not critical for stimulation of torpor expression but activation of specific somatostatin receptors is critical. This putative role for certain somatostatin receptor subtypes in torpor induction provides a promising new approach to unravel the endocrine mechanisms of torpor regulation.

Torpor in lactating Siberian hamsters subjected to glucoprivation

1998 ◽  
Vol 274 (1) ◽  
pp. R46-R51 ◽  
Author(s):  
Juliet L. Stamper ◽  
Irving Zucker ◽  
Daniel A. Lewis ◽  
John Dark
Keyword(s):  
Body Mass ◽  
Food Deprivation ◽  
Food Restriction ◽  
Rodent Species ◽  
Daily Torpor ◽  
Siberian Hamsters

Daily torpor has never been reported for any rodent species during lactation. To test whether torpor and lactation are incompatible processes, we administered 2-deoxy-d-glucose (2-DG), a glucose analog that interferes with cellular glycolysis, to Siberian hamsters during the 2nd wk postpartum. 2-DG (2,500 mg/kg of body mass) induced torpor in lactating as well as nonlactating females. Although depth of torpor did not differ between groups, duration of torpor tended to be shorter in lactating animals. Evidence of new milk bands suggests that pups were able to obtain milk from torpid dams. By contrast, dams subjected either to a combination of brief food deprivation and subsequent food restriction or just food restriction failed to display torpor, but instead cannibalized one or more pups. We conclude that torpor is possible during lactation; whether lactating dams in nature become torpid in response to energy shortages or cannibalize or abandon one or more of their offspring remains unknown.

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